I had asked in another thread about wearing a kevlar jacket, and the answer was it was allowed, provided that the airline would accept and that the state you're going allows wearing kevlar jacket.

But I was thinking of the risk of being shot by a stray bullet fired by a GTB. Against an opponent wielding a small pointy object, a chainmail would suffice. It is allowed everywhere (how would they do medieval reenactment fair ?) and isn't on the list of prohibited items. So, I assume (TSAMGR, feel free to shoot) that you can be a knight in shining armor on board. Feel free to charge anyone congregating near lavatories. Do not forget your warcry, it will make for an interesting in-flight entertainment.

Barring that, I suppose an inflatable jacket could protect you.

Irony aside, the linked article is obviously addressing the situation where there is indeed a clear terrorist attack onboard. However, I think intervening could hamper the work of the GTB and could result in you being shot. Better wait for the GTB to be taken down before attempting something stupid. And I am slightly frightened when reading this article just after the article about the NW flight posted all over FT. On other boards (not dedicated to flying), people are genuinely frightened and advocating physical action in case people are congregating in the aisle and lavatories. I was flabbergasted, and I thought of poor FTers congregating in the front of the plane on their way to a FT do...